Plant dermatitis is common and important as an industrial and recreational problem affecting thousands of persons each year and involving persons of all ages engaged in outdoor activities. Many thousands of Californian plants are capable of causing dermatitis, with at least 100 species reported to cause allergic contact dermatitis. One very important group of plants, the genus Phacelia (Hydrophyllaceae-Scorpion flower), consists of at least five species which have been reported by dermatologists to cause linear vesicles on exposed skin, very similar to poison-ivy or poison oak dermatitis. Due to the economic importance and lack of critical chemical studies of the allergenic phacelias, I propose to investigate five California species of scorpion flower and specifically (1) isolate and characterize the sensitizing constituent, (2) conduct a detailed scanning electron microscopy and chemical study of glandular hairs that are suspected of containing the allergen(s), (3) prepare Phacelia extracts (crude and pure) for patch testing in persons who have so-called poison-ivy dermatitis, and (4) distinguish persons who are sensitized to poison-ivy and scorpion flower so that appropriate hyposensitization can be ordered.